This invention relates to an image reading apparatus for scanning and optically reading document images and outputting them as electronic data. More particularly, this invention relates to an image reading apparatus equipped with two optical reading means for reading the images on the front and back sides of the documents or sheets fed one by one from a document reception tray by an automatic document feeder commonly known as an ADF.
Image reading apparatuses, normally called scanners, optically read the image of a document and convert the image into electronic data and transmit it to image forming apparatuses, such as personal computers, copy machines or facsimiles. There are following types of image reading apparatuses.
In the image reading apparatuses, there are a method wherein a thick document sheet, such as a book is placed on a platen formed above an image reading apparatus unit and this still document sheet is read by moving reading means, and a sheet throughput method wherein an automatic document feeder repeatedly feeds documents or sheets one by one from a supply tray to a platen at which still image reading means reads the documents as they move over the platen. Recently, the sheet throughput reading method has a function for simultaneously reading both the front and back surfaces of documents or sheets using two independent reading means on one transport path without requiring the documents to invert from front to back.
Examples of such sheet throughput image reading methods on image reading apparatuses that are equipped with two reading means to read the images on the front and back sides of the documents are disclosed in Japanese Patent Publications (KOKAI) No. 7-327111, No. 11-136444 and No. 11-32164.
In Japanese Patent Publication No. 7-327111, a platen for a still document situated above an image reading apparatus is used as a platen for so-called sheet throughput method to form a document transport path to feed and transport the documents to this commonly used platen. Also, two reading means opposingly arranged to sandwich the document transport path are used to read both the front and back surfaces of the documents that pass through this document transport path. Furthermore, one of the two reading means moves underneath the commonly used platen to read the still document manually placed upon the commonly used platen.
Also, in Japanese Patent Publication No. 11-136444, a platen for the still documents is located above an image reading apparatus, and a transport path for sheet throughput reading is located above the platen for the still documents. Also, between this platen for the still documents and the transport path, there is formed a light source for reading one surface of the document and a mirror to read the one surface of the document passing through the transport path, and on the opposite side of the light source and the mirror, reading means is arranged to read the other surface of the document.
Still further, Japanese Patent Publication No. 11-32164 discloses an image reading apparatus for reading both surfaces of the documents comprising a contact image sensor and optical reduction reading means above and below a document sheet transport path, wherein a document from a supply tray is inverted and transported to read one surface of the document that passes through a platen for sheet throughput disposed in the image reading apparatus; then the other surface of the document is read with reading means formed in the automatic document feeder at a side opposite to the platen for the sheet throughput; and the document is discharged to a discharge tray. Also, in the document sheet discharge direction of this image reading apparatus for reading both surfaces of the document, the platen for reading the still document is arranged such that the document manually placed thereupon is read by moving optical reduction reading means.
However, because both of the two reading means in the sheet throughput reading method of the image reading apparatus disclosed in Japanese Patent Publication No. 7-327111 employ an optical reduction reading method, there are problems such that the image reading apparatus that includes the automatic document feeder is larger and heavier.
Also, because in the image reading apparatus disclosed in Japanese Patent Publication No. 11-136444, the document sheet transport path, the light source for reading one surface of document sheets, the mirror and the reading means for reading one surface of document are formed in the automatic document feeder that opens and closes the platen for the still document, there are problems such that the image reading apparatus including the automatic document feeder is larger and heavier and the structure is complex.
In the image reading apparatus disclosed in Japanese Patent Publication No. 11-136444, the reading means for reading one surface of the document is arranged above (opposite side) the platen for reading the sheet throughput and the supply tray is arranged above the reading means for reading the other surface of the document, so there are problems such that the image reading apparatus including the automatic document feeder is larger. Furthermore, because it forms a U-shaped paper feed path to invert and transfer the document from the supply tray to the platen for the sheet throughput, the sheet passes through the platen for the sheet throughput reading to cause the sheet to endure an unusual posture and cause the sheet to flap when transferring into the platen for the sheet throughput and discharge. This makes it difficult to obtain quality reading of the images on the document. Also, there is a space wasted in the lower section in the vertical direction of the second reading means established in the automatic document feeder on the image reading apparatus, so the entire image reading apparatus including the automatic document feeder can not be made more compact.
An object of the present invention is to make the external shape of an image reading apparatus that is capable of simultaneously reading both the front and back surfaces of the document or sheet more compact and lighter in weight, and to provide an image reading apparatus that transports the document one by one in a stable manner using an automatic document feeder and that can provide quality image reading using two reading means opposingly arranged close to each other.